The present invention is directed generally to the centrifugal treatment of liquids, and more particularly to a structurally and functionally improved system for centrifugally separating liquid into fractions of different densities. The invention has particular application to the separation of components from whole blood and the present disclosure is directed primarily to this application. However, it will be understood that the system of the present invention is applicable to the treatment of other liquids and semi-liquid masses as well.
Intervivos blood processing, wherein whole blood is taken from a live donor, separated within a processing system into its constituent components, and then returned to the donor, has come into increasingly wide use during recent years. In the course of the processing predetermined portions of the separated blood components, which include plasma, red blood cells, white blood cells, and platelets, as well as subdivisions of these general categories, such as lymphocytes, glanulocytes, and reticulocytes, are either retained for storage or transfer to another patient, or are returned to the donor. Intervivos blood processing operations commonly performed in this manner include plateletpheresis, wherein the platelet component is separated; plasmapheresis, wherein the plasma component is separated; and leukopheresis, wherein the white blood cell components is separated.
Systems for carrying out intervivos blood processing typically include a separation chamber within which whole blood from a donor is subjected to a centrifugal force field. Because of differences in densities, the blood components are congregated in zones at different radial distances from the center of rotation of the separation chamber. Collection ports in the chamber remove the components from these zones for storage or recirculation.
One requirement of continuous flow intervivos blood processing systems is that the volume of blood in process within the system be kept as small as possible to minimize blood deprivement from the patient and the possibility of ill effects should operation of the apparatus be inadvertently interrupted. Furthermore, it is necessary that the flow defining portions of the system be sterile and disposable to minimize the possibility of contamination, and that the system and its associated centrifugation apparatus be simple to operate, and not require constant operator supervision. Certain prior art systems utilized processing chambers in the form of specially shaped bowls which required expensive manufacturing techniques and could not be formed by high volume production techniques. The system of the present invention provides a lower in-process volume than prior art sytems, and readily lends itself to automation to reduce operator requirements.
Another requirement of intervivos blood processing systems is that the processing operation be carried out as efficiently as possible at the highest possible flow rate to avoid unnecessary inconvenience to the patient. Previously, collection of ten standard units of platelets as defined by the Bureau of Biologics, U.S. Food and Drug Administration, required from 2 1/2 to 4 hours, whereas in the system of the present invention less than 1 1/2 hours are typically required to collect the same quantity of platelets.
Furthermore, the components separated by the processing system must be consistently high purity. In prior art systems the separated blood components were subject to intermixing, partially as a result of coriolis currents induced by rotation of the processing chamber, and partially as a result of inherent inefficiency in the separation process. The result of this intermixing was that a portion of the separated components had to be discarded, which had the effect of lowering the yield of the system. Typically, in prior art plateletpheresis applications a white blood cell component of from 15 to 20 percent was present in the derived platelet component. The present system provides a substantial improvement in the purity of the platelet component, typically providing a white blood cell component of less than2 percent in the collected platelet component.